1. Field of the Invention
The present invention relates to a play back apparatus for conducting the play back of a sound such as the music by the compression data in which the sound information (audio information) is high efficiently coded by a coding method such as the JPEG audio.
2. Related Art
Conventionally, there is a CD (compact disk) as a representative example of a recording medium of the audio information such as music. In this disk, the audio information is held by pit rows spirally formed in high density on a single surface of the 12 cm diameter disk, and by optically reads out the information by a CD player as a play back apparatus, the binary coded digital signal is generated corresponding to the pit shape, and the play back of the audio can be conducted according to the signal. In the CD, the music of maximum 74 minutes of 2 channels per each disk can be recorded as the non-compressed digital audio data by so-called the linear PCM (Pulse Code Modulation), and the CD is widely used as the recording medium which is small sized and has the good portability.
Further, recently, a recording medium which has a greatly smaller size and more excellent portability, and in which a larger amount of audio information, than the above CD, can be recorded, and its play back apparatus are required, and as an example, a solid state memory as the recording medium in which the audio information is recorded as the compression data, and a play back apparatus such as so-called solid player to play back the audio information such as the music according to the compression data stored in the solid state memory, are proposed.
In the compression data, there is the compression bit stream data which is coded by, for example, MPEG audio method. FIG. 13 is a rough sketch+showing an example of a physical format of the compression bit stream data by the MPEG audio method, and herein, this drawing is shown in the data format coded by MPEG-4 Twin VQ which is one of the MPEG-4 Audio GA coding.
As shown in FIG. 13, the compression bit stream data of the method according to the conversion coding such as the MPEG-4 Twin VQ is structured by a format in such a manner that the bit rows as the result in which a predetermined number of samples of the audio information are collected and grouped to 1 frame, and are compression coded, continue for each frame. The compression bit stream data is structured by a fixed length frame in which fixed bits are allotted to each frame. Further, herein, a case is supposed in which, in a top of each frame, a header area having a frame synchronous word or the information to control the operation mode of the decoder is provided, and in the header, a frame number N (=1, 2, 3, 4, . . . N, N+1, . . . ) expressing the continued order of each frame of the compression bit stream data is included. Further, in the compression bit stream data possessed by each frame, the quantification index information for decoding the MDCT coefficient, and the window information required when the MDCT is inversely converted, and the spectrum envelope and the gain quantification parameter information are included.
Such the compression bit stream data is sent to the personal computer from, for example, the distributor of the data through the internet, and when the user down-loads this data into the fixed memory mounted in the personal computer, the data is stored in the fixed memory as the audio information.
Then, when the solid state memory in which the audio information is stored as described above, is mounted in the play back apparatus by the user, and the play back command of the audio information is given, in the play back apparatus, the control section conducts the control to successively read out the compression bit stream data stored in the solid state memory corresponding to the command, in the buffer memory, and to supply it, and a predetermined amount of data is accumulated once in the buffer memory, and after that, the data accumulated in the buffer memory is successively supplied intermittently from the buffer memory to the compression decoder for each of continued predetermined frame number units.
The compression decoder makes the data of the predetermined frame number units supplied from the buffer memory, synchronize with the header of each frame, and reads-in it for each frame and conducts the decoding conversion processing, and after that, successively generates the non-compression PCM audio data according to the decoding conversion processing. The generated PCM audio data is sent to the D/A converter, and is conversion processed into the analog audio signal and supplied to an amplifier. The amplifier amplifies the analog audio signal and supplies to a speaker. As the result, the play back sound of the music corresponding to the analog audio signal is produced from the speaker.
Further, while the play back apparatus plays back the music, when the user continues the pressing of the quick traverse command (FF command) button provided on the playback apparatus, the quick traverse play back command is given, and after that, when the user stops the pressing of the FF button, the quick traverse play back command is released, and the play back apparatus returns to the ordinary play back operation again.
When the quick traverse play back command is given while the play back apparatus plays back the music, the control section of the play back apparatus interrupts the decoding conversion processing of the compression decoder corresponding to the start of the FF command by the pressing operation of the FF command button, and stops the output from the compression decoder, thereby the control section interrupts the play back of the music, and starts the measurement of the elapsed time from the FF command start. Accordingly, while the play back apparatus conducts the quick traverse play back operation, the play back apparatus becomes a silent condition in which the sound is not played back from the speaker of the play back apparatus.
Further, when the quick traverse play back command is released by the release of the FF command, after the control section calculates the elapsed time from the start of the FF command to the release, the control is conducted in such a manner that the frame position of the data read from the solid state memory is changed to the position preceded by the frame number proportional to the elapsed time, and it is started that the data from the frame position is successively supplied to the buffer memory.
The control section causes to start again the supply of the data from the preceded frame position to the compression decoder, from the data accumulated in the buffer memory, corresponding to the release of the FF command, and the decoding conversion processing of the data from the frame position is started again also for the compression decoder, and the PCM audio data from the frame position is supplied to the D/A converter, and the analog audio signal is generated, and supplied to the amplifier. The amplifier current-amplifies the supplied analog signal, and the mute release of the play back sound is conducted, and the sound is supplied to the speaker. As the result, the play back apparatus can start again the play back of the music from the frame position of the quick traversed data.
[Problems to be Solved]
As described above, while the play back apparatus plays back the music by the compression bit stream data from the solid state memory, and during the quick traverse playback operation from the start of the FF command by the user to the command release, because the play back sound is not played back from the speaker of the playback apparatus, the user can not easily confirm successively what amount of data is quickly traversed by the play back apparatus, by the comparison of the quick traverse sound in the hearing sense. Accordingly, there is a problem that the user has the increased feeling of uneasiness regarding whether the quick traverse play back operation of the apparatus is normally conducted during the quick traverse command.
The above problem occurs also in the case where, for example, while the play back apparatus plays back the music, when the user continues pressing of the quick returning (REW) button provided on the play back apparatus, the quick returning play back command according to the quick returning command (REW command) is conducted.
For such the problem, in the case where the play back apparatus is given the quick traverse play back command (or quick returning play back command), when N multiple speed play back (or N multiple speed reversal play back) whose speed is higher than the ordinary play back speed, is conducted, and when each portion of the play back apparatus is structured so that the play back sound (or reversal play back sound) whose speed is N times higher, is outputted from the speaker, the problem can be solved, however, in that case, it is not only necessary that the control section conducts the control to increase the complicated decoding conversion processing speed of the compression decoder, by making adjustment to increase the synchronous speed of the PCM clock so that the data processing speed in each section of the apparatus is increased, but, it is also necessary that the whole play back circuit of the apparatus is also structured so that the play back speed is stably switched without any trouble, and as the result, because the structure of each section of the apparatus becomes complicated, and the cost is greatly increased, it is not practicable.
In view of the above problems, the present invention is attained, and the object of the present invention is to provide a play back apparatus in which, in the play back apparatus which plays back the audio information by the compression audio information, when the quick traverse play back command (or the quick returning play back command) is given, by playing back the special sound in which the quick traverse play back sound (or the quick returning play back sound) is converted into an imitation sound, the user can easily confirm in the hearing sense that the apparatus is conducting the quick traverse processing (or the quick returning processing) of the data.